With the known hydraulically operated coupling elements (clutches and brakes) through which coolant and lubricant oil is circulated, the flow in the clutch and brake of the oil is mainly left to the effect of gravity on the oil. There are also systems wherein the rotating clutch housing forms inside the housing an inertially acting oil ring. The dip tube projecting from this oil ring produces the oil circulation to the coupling elements, that is through the brake housing and the mount (tube shaft). Naturally it is a disadvantage that in order to create sufficient centrifugal force to pump the oil a certain minimum rotation rate is necessary. Thus this solution is limited to coupling elements with a high rotation rate (control drives, drives on slow shafts, e.g. eccentric shafts).
In addition the effectiveness is very strongly dependent on temperature because of the viscosity characteristics of the oil used for cooling and lubricating. As a result on starting up the apparatus and when the oil is cold there are substantial problems in the coupling operation (sticking of the oil-bathed disks on braking to produce a pulsation) and in the seal of the coupling elements that are relatively sealed with a labyrinth. As a result of the poorer oil flow on startup it can happen in extreme cases that the entire oil content of the container serving to drive the coupling elements (hydraulic supply) is forced into the coupling elements and thus the monitored oil level in the container causes the machine to shut down even before oil circulation has started. This is countered by providing expensive heating systems for preheating the oil along with large-capacity supplies.